NASA/UC Study: Warming Ocean Shown to Melt Ice Sheets From Below

A new study produced in Science shows that a warming ocean is causing at least 55% of the ice melt seen in Antarctica.

The study, run by NASA and Eric Rignot at the University of California, Irvine, shows that basal melting, or melting from below, was responsible for a majority of Antarctic melt. Contact with warm ocean currents was found to erode the ice in a way that was previously undetected. Warming waters, driven by wind and currents, swept against the ice at numerous locations on the ice shelves’ underbellies, carrying away larger and larger volumes of glacial melt.

Until recently, this process was invisible and, therefore, not included in the science of ice sheet dynamics.

The ice shelves, which act as stoppers keeping interior glaciers from sliding into the ocean, are critical to keeping the Antarctic ice sheet healthy. So discoveries of how ice sheets melt are of key importance to both glacial and climate science. And the fact that warming oceans are eroding the ice from underneath is some cause for concern. From NASA:

Antarctica holds about 60 percent of the planet’s fresh water locked into its massive ice sheet. Ice shelves buttress the glaciers behind them, modulating the speed at which these rivers of ice flow into the ocean. Determining how ice shelves melt will help scientists improve projections of how the Antarctic ice sheet will respond to a warming ocean and contribute to sea level rise. It also will improve global models of ocean circulation by providing a better estimate of the amount of fresh water ice shelf melting adds to Antarctic coastal waters.

The image below, compiled by NASA and based on the study’s findings shows how ocean-driven melt rates compare to glacial calving. Overall melt rates are indicated by the red-to-blue color shift and related scale in the upper left corner of the image.

The study built on previous findings in Nature showing that wind-driven ocean currents played a major role in ice sheet melt. Together, these results are challenging previous understandings of ice sheet melt. Past analysis of ice sheet health had assumed that most ice losses occurred during glacial calving events. What Rignot and Pritchard (author of the Nature study) found was that ocean-glacier interaction was a more important factor in overall ice melt.

“This was quite a big gap in our understanding of how the ice sheets interact with their surroundings, and what it shows is that the oceans play a bigger role than we’d previously thought,” said Pritchard about the new study’s results in a Scientific American interview.

Melt From Below

That a warming ocean is a powerful driver of ice melt makes sense. Water contains more heat energy than air and so a given volume of water at a given temperature would have more potential to melt ice than the same volume of atmosphere. Pritchard and Rignot’s findings have major implications for modeling ice sheet melt and could help improve global models. They may also lead the way to a better understanding of ice melt in general.

Sea ice model melt forecasts have also suffered due to a lack of understanding of how the ocean interacts with floating ice. This missing data has led the models to vastly under-estimate sea ice melt in the Arctic. It has also resulted in a general failure in the understanding of how storms affect sea ice floating on the surface of a warming ocean. Scientists and forecasters also often down-play or ignore the impact warm water upwelling, churning or ice sheet contact with warming water currents can have on overall melt rates.

The Pritchard and NASA/Rignot studies of basal melt in Antarctica may, therefore, have broader implications for understanding ice melt around the globe. Most large continental glaciers have contact with the ocean and the sea ice floats on the ocean surface. A dynamic interaction between the ice and ocean is, therefore, ongoing. So improvements to understandings of this interaction are likely to better resolve our forecasts for future melt.